Cast metal wire of reduced porosity

ABSTRACT

In the continuous casting of molten metals to form filamentary wire by extruding the melt through an orifice as a molten stream which is then solidified to a solid wire product, the porosity of the resulting cast wire product is greatly reduced when the extrusion velocity exceeds about 2400 feet per minute. Case wire of various steel alloys have been obtained with porosities less than 0.06 volume percent.

United States Patent Dobo 1451 Sept. 9, 1975 [54] CAST METAL WIRE OF REDUCED 3,658,979 4/1972 Dunn et al. 164/66 POROSITY 3,715,419 2/1973 Privott, Jr. eta1...... 164/82 [75] Inventor: Emerick J. Dobo, Cary, NC.

Primary ExaminerW. Stallard [73] Asslgnee' Monsanto Company LOUIS Attorney, Agent, or Firm-Russell E. Weinkauf [22] Filed: Dec. 7, 1973 Appl. No.: 422,933

Related U.S. Application Data Continuation-impart of Ser. No. 319,133, Dec. 29, 1972, Pat. No. 3,81 1,850.

U.S. Cl 29/193; 164/82 Int. Cl. B21C 37/04; B22D 11/00 Field of Search 29/193; 164/82 References Cited UNITED STATES PATENTS 66 3/1959 Pond 164/82 [5 7] ABSTRACT In the continuous casting of molten metals to form filamentary wire by extruding the melt through an orifice as a molten stream which is then solidified to a solid wire product, the porosity of the resulting cast wire product is greatly reduced when the extrusion velocity exceeds about 2400 feet per minute. Case wire of various steel alloys have been obtained with porosities less than 0.06 volume percent.

3 Claims, 3 Drawing Figures PATENTED 3E? 75 FIG.3.

FIG.2.

CAST METAL WIRE OF REDUCED POROSITY CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my copending and commonly assigned application, Ser. No. 319,133, filed on Dec. 29, 1972, and now US. Pat. No. 3,81 1,850.

FIELD OF THE INVENTION The invention relates to cast wire products of novel character. More particularly, the invention relates to fine diameter cast wire having a greatly reduced porosity and a means by which it may be obtained. By fine diameter wire there is meant a wire product having a diameter of less than about 35 mils.

BACKGROUND OF THE INVENTION The continuous casting of molten metals as free castings, i.e., without molds, to form filaments and wire has come to be known as inviscid spinning. In such casting, the essentially inviscid melt of a metal is extruded through an orifice to produce a stream of molten metal which is then solidified to a filamentary wire product.

US. Pat. No. 3,658,979 incorporated as a part of this description by way of reference sets forth the basic precepts by which filaments and wire may be formed through an extrustion of essentially inviscid melts. In brief, a low viscosity melt is extruded through an orifice at an appropriate velocity into a selective atmosphere. When the hot jet issuing from the extrusion orifice contacts the atmosphere a reaction occurs which results in the formation of a film or protective sheath about the jet surface. This film, called the stabilizing film, stabilizes the filamentary jet or stream against break-up from the forces of surface tension until sufficient heat can be removed to effect a phase change to the solid state. The stabilizating film must, of course, be formed very rapidly. Moreover, the film must be in the solid state at the high temperatures in which it is formed. The film must also be substantially insoluble in the molten jet at the extrusion temperatures to insure continuity of its function.

Although this process offers great potential, full realization of such potential has been thwarted by an inability to raise the rate of filament productivity beyond the level of 1300-1400 feet per minute. Moreover, it has not been possible in the past to reduce the porosity of the resulting cast wire product to acceptable limits for many important end uses. Because of a consistently high porosity in the wire produced the important porperties of tensile strength, ductility and fatigue resistance were adversely affected and severely impaired.

Accordingly, it is a principle object of this invention to provide a cast wire product in which the degree of porosity is at a reduced level not heretofore attained in cast wire.

It is a further object of this invention to provide an improved method and apparatus for extruding filamentary wire from molten metal which permits drastically increased rates of productivity and wherein the porosity of the wire produced is greatly reduced.

SUMMARY OF THE INVENTION It has now been surprisingly discovered that the porosity of wire produced by the extrusion of molten metal is influenced by and can be greatly reduced when the extrusion is conducted at very high velocities. That is, substantial reductions in porosity have been found to occur when extrusion velocities in excess of 2,400 feet per minute are employed.

Although extrusion speeds of this magnitude have not previously been attainable, they are now brought to realization by an improved process which comprises the following steps in sequence: l) extruding continuously a metal melt through a shaping die to form a filamentary jet; (2) passing the filamentary jet immediately upon issue from the shaping die into a zone occupied by a pressurized gas; (3) forwarding the jet in cocurrent flow with the pressurized gas through a supersonic nozzle and intoa first zone occupied by a gaseous atmosphere capable of causing a film to form about the jet surface by reaction therewith; thence (4) passing the filamentary jet through a converging passageway into a second zone occupied by the film forming atmosphere.

An apparatus by which this procedure may be carried out will be best understood by a description of the accompanying drawings in which:

FIG. 1 is a schematic vertical crosssection of a typical filament extrusion apparatus employing a novel orifice assembly.

FIG. 2 is an enlarged,-partial view of the orifice assembly of FIG. 1.

FIG. 3 is an enlarged partial view of the gas plate orifice in the orifice assembly of FIG. 1.

DESCRIPTION OF THE DRAWINGS FIG. 1 depicts a crucible 10 enclosing a quantity of molten essentially inviscid material 11. Functionally as part of the base of crucible 10 is an orifice plate 12 having an extrusion orifice 13. Spaced beneath plate 12 is a gas plate 14 having a convergent-divergent shaped orifice 15 which is aligned substantially coaxial with orifice 13. Plates 12 and 14 define an essentially enclosed chamber 16, which can be referred to as an attenuating gas zone.

Beneath gas plate 14 is a third plate 17 hereinafter called a stream control plate. Stream control plate 17 has an orifice or throat 18 which is aligned substantially coaxial with throat 15 (and consequently with orifice 13). The walls of orifice 18 converge in the direction of its exit with the included angle of convergence being between 7 and 20 degrees. Stream control plate 17 and gas plate 14 define a second substantially enclosed chamber 19, which can be referred to as a first reactive gas zone. Pedestal 20 supports the entire apparatus and also defines cavity 21, which can be referred to as the second reactive gas zone, since the molten jet further reacts therein with a film forming gas.

In operation, a positive pressure head is supplied to molten material 11, by means of a pressurized gas. The jet 22 is thus caused to issue from the extrusion orifice 13 into chamber 16. Chamber 16 is provided with a quantity of attenuating gas which is supplied under pressure through gas line 23. The attenuating gas is constrained to move laterally between orifice plate 12 and gas plate 14 and thus contacts the emerging jet 22 in a direction initially normal to the path of jet 22. This flow is in a large measure self-distributing toward symmetrical flow. The attenuating gas then flows cocurrently with jet 22 through the gas plate throat l5 and into chamber 19. The nature of the attenuating gas is not critical. Generally, an inert gas such as helium or argon is used. However, in some instances it may be desirable to employ a mixture of inert gas with a gas such as described below which is capable of forming a film about the jet surface.

Chamber 19 is provided with a quantity of gas reactive with jet 22 via gas line 24. The reactive filmstabilizing gas contacts jet 22 at the entrance of orifice l8 and is at a flow rate sufficient to penetrate the shroud of attenuating gas which has been caused to envelope the jet as it issues from gas plate orifice 15. A fiirther quantity of reactive gas is supplied by gas line 25 into cavity 21 for contact with jet 22 proximate to the exit of orifice 18. The nature of the reactive gas is not critical so long as it is capable of forming a film about the surface of molten jet 22. In many instances oxidizing gases such as carbon monoxide and air have been successfully employed. For other suitable filmforming gases that may be used see US. Pat. No. 3,658,979.

FIG. 2 illustrates the general geometrical relationship between plates 12, 14 and 17 together with their respective orifices. Although the diameter of the throat section (most narrow section) of gas plate orifice 15 may be larger than the exit diameter of extrusion ori fice 13, best results are obtained when it is of an equal or lesser diameter than that of the exit of orifice 13. Particularly good results may be obtained when the ratio of the exit diameter of orifice 13 to the throat diameter of orifice 15 lies in the range of from about l.0:l.0 to 15:10 The length of orifice 15 is generally maintained at from about 5 to lOO times greater than the exit diameter of orifice 13. As noted, orifice l8 converges in the direction of its exit at an included angle of from about 7 20. It is generally desirable although not critical that the entrance diameter of orifice 18 be from about 2 to 5 times larger than the throat diameter of gas plate orifice 15.

The gap distance of gap 31 between orifice plate 12 and gas plate 14 should be substantially equal to the diameter of gas plate throat 15. On the other hand, the dimensions of gap 32 between gas plate 14 and stream control plate 17 is not considered to be critical. However, enough space should be provided to accommodate a sufficient quantity of reactive gas to penetrate the inert gas which flows co-currently with jet stream 22. Generally, it has been found that a gap distance of from about 5 to 20 mils between gas plate 14 and stream control plate 17 in the vicinity of their respective orifices is satisfactory.

FIG. 3 illustrates gas plate 14 and its shaped orifice schematically in an enlarged vertical section. The entry area or convergent section 28 is rounded gently to reduce friction. The extent of convergence is not critical, it being merely necessary that the orifice walls converge in some degree at the entry. The convergence terminates at throat section 29 from where the walls diverge to form divergent exit section 30. The included angle of divergence in this section should be between 4 and 12, with from 6 to 8 being of preference for attenuation at the higher speeds. Best results are achieved when divergent section 30 is of greater length than convergent section 28, and particularly when the length is from 10 to times greater. Arrows 26 and 27 illustrate the flow paths of the attenuating and reactive stabilization gases, respectively.

The materials which are utilized in fabricating the plates which comprise the orifice assembly of this invention should be essentially inert, each to the other, under the conditions employed during extrusion. Moreover, the materials must be resistant to thermal shock and have sufficient strength to withstand the substantial mechanical stresssimposed by the extrusion process. For example, in the extrusion of metals such as copper and ferrous alloys, it may be preferable to use ceramic.

materials such as high density alumina, beryllia, and zirconia. For high temperature extrusion using ceramic charges, materials such as molybdenum and graphite can be employed. For extrusion processes involving lower temperatures, stainless steel assemblies have been found to perform well.

The various wire products which are obtainable in accordance with this invention have a myriad of practical uses. Perhaps one of the more important examples is the use of filamentary steel as a reinforcement element in the manufacture of modern automobile tires as well as tires for other vehicles.

In the production of filamentary steel wire by these methods an oxygen-containing gas is employed as the stabilizing medium into which the molten stream is extruded to form the enveloping film which protects the liquid stream against surface tension break-up until solidification can occur. In order that the stabilizing film be capable of functioning in the intended manner, the oxide formed must be stable and insoluble in the melt. Because the oxide of iron does not possess these properties, it is necessary that a second alloying metal be added to the melt before steel can be satisfactorily processed. That is, a second metal is added whose oxide is stable and insoluble in the molten charge. Various metals may be used for this purpose and include among others magnesium, beryllium, chromium, lanthanum, titanium, aluminum and silicon, with aluminum and silicon' being generally preferred. The second metal is present in only very minor amounts ranging from about 0.3 to 6.0 percent on the weight of the alloy. When employing aluminum, it is generally present in an amount of from 0.3 to 5.0 percent while silicon is preferably employed in an amount of from 0.5 to 6.0 percent on the weight of the alloy.

The following example illustrates a production run in accordance with this invention to produce wire from a steel-aluminum alloy. I

EXAMPLE I An apparatus such as depicted in FIG. 1 was employed to form filaments by extruding the melt of steel alloyed with 1.0% by weight of aluminum at a realized production rate of 3500 feet per minute.

The orifice assembly used was of a design as typified by F IG. 2 of the drawings. The orifice plate 12 was 125 mils in both length and diameter, i.e., having an aspect ratio L/D of l. Gas plate 14 was also l25 mils thick with the throat of the supersonic nozzle 15 therein being 8 mils in diameter or equivalent to the diameter of filament shaping orifice 13. Stream control plate 17 was 62 mils thick and orifice 18 therein had an exit diameter approximately four times that of the throat diameter of convergentdivergent orifice 15. An included angle of 15 was formedby the converging walls of orifice l8.

In operation, an argon gas head pressure of p.s.i.g. was used to force the melt through the orifice of extrusion plate 12 to form a filamentary jetemerging into gap space 16 between plates 12 and 14. Gap 16 was supplied with helium at a pressure of 76.8 p.s.i. g. and at a flow rate of 301 cm lmin (STP). The pressurized helium contacted the jet, at an angle normal to its path of movement and then flowed cocurrently with the jet through supersonic nozzle in gas plate 14. 'Upon' exit from nozzle 15, the filamentary jet entered gap space 19, which was supplied with carbon monoxide as the film-forming gas. The carbon monoxide flow rate into gap space 19 was 5080 em /min (STP). The jet then passed through stream control orifice '18 and into cavity 21 where' additional carbon monoxide was' supplied at a rate of 1630 cm /min (STP). The film stabilized jet which solidified upon cooling was then taken up as a filamentary product. During the course of this high-speed extrusion, the molten jet remained continuous and did not deviate from a straight path.

An eighteen fold increase in power is required to achieve a 3500 ft/min. production rate when compared with 1350 ft/min. the optimum attainable by prior practice. By the method of this invention most of the power needed comes from the pressure drop across the gas plate. A large pressure drop occurs as a result of the flow of the pressurized inert gas through the supersonic or convergent-divergent nozzle orifice of the gas plate. In addition to exerting a piston-like pressure on the molten stream, expansion of the gas in the nozzle contributes substantially to the velocity of the stream or jet. That is, with a large pressure drop there is a corresponding reduction in the enthalpy of the gas. In all probability the energy released is initially transferred to the gas and then through viscous drag a part of it is in turn transferred to the molten stream where it acts to power a velocity increase. Calculations show only a small percentage (less than 5%) of the enthalpy released by the gas through pressure drop in the gas plate is converted to kinetic energy of the filamentary jet. Even with this poor conversion, approximately onethird to one-half of the power contained in the jet, when extruding at 3500 ft/min., comes from this conversion of enthalpy. Because the thermodynamics of the gas as it passes through the gas plate plays such a large role in speeds attained, it is necessary that there be only a moderate increase in the applied gas pressure over that of conventional systems for achieving the high jet velocities of this invention.

The following example illustrates the production of wire from a steel-silicon alloy in accordance with this invention.

EXAMPLE II Steel containing 5% silicon at a temperature of 1432C. was extruded through a 9 mil orifice held at a temperature of 1440C. using a head pressure of 80 p.s.i.g. The pressure of the attenuating gas was 68 p.s.i.g. to give a 12 p.s.i.g. gradient across the orifice. The melt flow was 65 grams/minute. The attenuating gas supplied at gap 16 and composed of 68% carbon monoxide and 32% helium, entered at a rate of 368 cc/minute (STP). The primary carbon monoxide flow supplied at gap 19, was 0.8 liter/minute. The carbon monoxide flow to the cavity 21 was shut off. The helium coolant flowed to the cooling column at the rate of 268 liters/minute. Wire, 4.1 mils in diameter, was obtained. The wire was flexible and readily tied into knots without breaking. The surface was bright and in Examples 1 and II.

-"microscope, a mini-computer'and a television camera where the electrical output from the camera is fed into a closedwircuit television monitor that displays the image. The image is scanned by parallel, evenly-spaced lines of the scanning system. The signal produced represents the intensity profile of the image. This signal is next processed by the detection circuit, and the result is a binary signal that very precisely defines the selected feature. The output from the detector which consists only of signal pulses from the detected features is channeled into the TV monitor to allow a visual control of the features to be detected. The detectors output signal is also passed into the computer where the porosity measurements are instantly derived from the signal and recorded on the computer readout. In conducting the test measurements polished longitudinal sections of the wire are placed upon a specimen block and inserted in the sample holder of the microscope. After proper focusing, 15 scans are made and the results averaged.

In Table I below tensile and porosity measurements are given on filamentary wire obtained in test runs to produce wire from a steel-aluminum alloy. Filaments comprising steel alloyed with 1.0 percent by weight of aluminum were spun on the equipment of this invention at speeds in excess of those previously attainable. The control was spun on conventional equipment at the highest rates permitted. The results follow:

TABLE I Speed Tensile Porosity (fpm) (lbs/2 in. avg) (volume control 1300-1400) 240,000 0.10 3000 264,000 0.06 3500 (Example 1, above) 248,000 0.05 3725 244,000 0.04

the maximum rates permitted.

TABLE 11 Speed Porosity (fpm) (volume 7:)

control (1350) 0.110 2 0.025 2800 0.010

TABLE II-Continued Speed Porosity (fpm) 7 (volume 3200 (Example ll, above) 0.006 3660 0.003

metal alloys.

I claim: g 1; A finediameter ca st wire product consisting of an 5 alloy of steel a porosity l ess than 0.06 volume percent,

'- 2. The-fine diameter cast wire product of claim 1,

'wherein said alloy consists of steel alloyed with from 0.3 to 5.0 percent by weight aluminum;

3. The fine diameter cast wire product wherein said alloy consists of steel alloyed with from by weight silicon.

0.5 to6.0 percent of claim 1, 

1. A FINE DIAMETER CAST WIRE PRODUCT CONSISTING OF AN ALLOY OF STEEL AND HAVING A POROSITY LESS THAN 0.06 VOLUME PERCENT.
 2. The fine diameter cast wire product of claim 1, wherein said alloy consists of steel alloyed with from 0.3 to 5.0 percent by weight aluminum.
 3. The fine diameter cast wire product of claim 1, wherein said alloy consists of steel alloyed with from 0.5 to 6.0 percent by weight silicon. 